This invention pertains to a tape spool assembly, and more particularly to a coaxial, interbiased, two-spool assembly for handling magnetic recording tape, or the like. For the purpose of illustration herein, a preferred embodiment of the invention is described in conjunction with a tape deck in a telephone answering device wherein the invention has been found to have particular utility.
There are many applications in which it is desired to utilize tape transport apparatus which is simple, reliable, and as compact as possible. For example, a modern telephone answering device of the type which might be used in a small office or in a home is one type of apparatus in which these characteristics are particularly desirable.
One technique which has been used in the past to approach these objectives is to use a stacked, or coaxial, double spool assembly for collecting the opposite end of the tape in the usual windings. With such an assembly, there is conventionally provided a single spirally wound biasing spring, such as a clock spring, one end of which acts directly on one of the spools, and the other end of which acts directly on the other spool, tending to produce counterrotation between the spools. The purpose of such a spring is to maintain tension in the reach of tape which extends between the spools (along guide means and adjacent the usual recording, playback, and erase head), as well as to accommodate limited relative rotation between the spools to take care of differences in the diameters of windings on the spools as the tape is moved in reverse directions.
However, this type of construction has not been entirely satisfactory. To begin with, employing a single spring between spools does not, without seriously compromising overall compactness, permit use of a long enough spring to accommodate a relatively long run of tape on the spools. In other words, where long tape runs are desired (for example, a tape run accommodating perhaps up to about twenty minutes of recording), it is necessary to employ so long a spring, that the space required for this spring dictates the use of relatively sizable spools. A further problem is that where a single spring is used, this spring will be quite relaxed with most of the tape collected as windings on one of the spools, but will be extremely tense in the reverse situation where most of the tape is collected as windings on the other spool. As a consequence, as the tape is driven in reverse directions, tension in it varies extremely widely. This situation causes a number of very undesirable events. For example, it tends to produce inordinately high tape wear. Further, and particularly where the spring is especially tense, this produces considerable friction between the tape and the guide means for it, which friction can produce effects known as "wow" and "flutter."
A general object of the present invention is to provide a unique, interbiased, coaxial, double spool assembly which offers all of the features mentioned above as being desirable, while at the same time avoiding the several problems just discussed encountered with conventional interbiased spool assemblies.
According to a preferred embodiment of the invention, what is proposed is a tape spool assembly of the type just generally outlined, which includes a pair of coaxial spools that are interbiased for counterrotation by a pair of axially spaced, spirally wound biasing springs. Featured in the invention is a floating rotatable plate which is disposed between the spools, and is adapted for rotation relative to both spools and on the same common axis with the spools. The faces of the spools which confront this plate are provided with central cylindrical wells in which are disposed the two biasing springs. One of these springs acts between the spool containing it and one side of the floating plate, and the other spring acts between its associated spool and the opposite side of the floating plate.
With this construction, one gains the advantage of using a relatively long spring, and hence the ability to accommodate relatively long recording times, without the disadvantage of having to wind a single spring in a single compartment, with attendant compromise of compactness. Further, with the two springs which are used according to the invention mounted as just generally described, overall tension in that reach of tape which extends between the spools is maintained relatively constant. Thus, the wear and friction problems mentioned above are greatly minimized. In particular, tension in the springs, and hence in a tape, toward either limit of movement of the tape is greater than at intermediate positions. This is to be contrasted with the situation surrounding use of but a single spring which tenses toward one extreme of tape movement, and relaxes toward the opposite extreme.
These and other objects and advantages which are attained by the invention will become more fully apparent as the description which now follows is read in conjunction with the accompanying drawings.